1. Field of the Invention
This invention relates to compositions and methods for the treatment of graft-versus-host disease, and more specifically to the administration of inhibitors of adenosine deaminase such as pentostatin and analogs and derivatives thereof.
2. Description of Related Art
For dysfunctional and/or diseased organs of the body, besides therapeutic invention with drugs, organ transplantation is an alternative, sometimes the last resort in the treatment of the patient. Particularly for patients with leukemia, end-stage renal, cardiac, pulmonary or hepatic failure, organ transplantation is quite commonly used in the treatment. For example, allografts (organ grafts harvested from donors other than the patient him/herself or host/recipient of the graft) of various types, e.g. kidney, heart, lung, liver, bone marrow, pancreas, cornea, small intestine and skin (e.g. epidermal sheets) are currently routinely performed. Xenografts (organ grafts harvested from non-human animals), such as porcine heart valves, are also being used clinically to replace their dysfunctional human counterparts.
To ensure successful organ transplantation, it is desirable to obtain the graft from the patient's identical twin or his/her immediate family member. This is because organ transplants evoke a variety of immune responses in the host, which results in rejection of the graft and graft-versus-host disease (hereinafter, referred to as “GVHD”).
The immune response is primarily triggered by T cells through recognition of alloantigens, and the major targets in transplant rejection are non-self allelic forms of class I and class II Major Histocompatibility Complex (MHC) antigens. In acute rejection, donor's antigen-presenting cells such as dendritic cells and monocytes migrate from the allograft to the regional lymph nodes, where they are recognized as foreign by the recipient's CD4+ TH cells, stimulating TH cell proliferation. Following TH cells proliferation, a population of effector cells (including cytotoxic CD8+ T cells and CD4+ T cells) is generated, which migrates and infiltrates to the graft and mediates graft rejection (Noelle et al. (1991) FASEB 5(13):2770).
Whereas acute rejection is a T cell-dependent process, a broad array of effector mechanisms participates in graft destruction. Through the release of cytokines and cell-to-cell interactions, a diverse assembly of lymphocytes including CD4+ T cells, CD8+ cytotoxic T cells, antibody-forming B cells and other proinflammatory leukocytes, is recruited into the anti-allograft response. Antigen-presenting graft cells are destroyed directly by cytotoxic CD8+ T cells. Activated CD4+ T cells produce interleukin-2 (hereinafter, referred to as “IL-2”), which is essential to the activation of both CD8+ T cells and B cells. Additionally, CD4+ T cells produce other cytokines such as IFN-γ and IL-4 that also contribute to the destruction of allograft. Furthermore, interferon-γ (hereinafter, referred to as “IFN-γ”) induces increased expression of class I and class II MHC molecules on graft tissue, which is more readily attacked by alloreactive effector cells. IFN-γ enhances macrophage activity and affects many inflammatory cells. leading to delayed-type-hypersensitivity reaction and inflammation causing nonspecific damage to the graft. These reactions appear to be the primary cause of the early acute rejection that may occur within the first few weeks after transplant. If untreated, acute rejection progresses to a rapid and severe process that causes destruction of the transplant within a few days.
On the other hand, when a T-lymphocyte from the donor recognizes the differences based on a set of genetic markers, generally referred to as human leukocyte antigens (HLA), and it starts to attack the new body, i.e., the patient's body. Although most patients and donors are matched as closely as possible for HLA markers. Many minor markers, however, differ between donors and patients except when the patient and donor are identical twins. Before a transplant, extensive typing of the donor and recipient is performed to make sure that the donor and recipient are very close immunologically.
Despite this typing there are immunological differences that cannot be detected and that the T-lymphocytes in the donor graft are capable of detecting. As a result, the donor T-lymphocytes start to attack the patient's body and cause GVHD.
There are two forms of GVHD: the acute and chronic GVHD. Acute GVHD usually occurs within the first three months following a transplant. T-cells present in the donor's bone marrow at the time of transplant attack the patient's skin, liver, stomach, and/or intestines. The earliest signs of acute GVHD are usually a skin rash that appears on the hand, feet and face. Other than blistering skin, patients with severe GVHD also develop large amounts of watery or bloody diarrhea with cramping due to the donor's T-cells' attack on the stomach and intestines. Jaundice (yellowing of the skin and eyes) is the usual indication that GVHD disease involves the liver. The more organs involved and the worse the symptoms, the worse the GVHD disease.
In the case of bone marrow transplantation, in particular, GVHD is another obstacle to survival of transplanted patients. Storb (1984) “Pathophysiology and prevention of graft-versus-host disease.” In Advances in Immunobiology: Blood cell antigens and bone marrow transplantation, McCullogh and Sandler, editors, Alan, Inc., N.Y., p. 337. A large proportion of GVHD-afflicted individuals dies as a result of GVHD. Weiden et al. (1980) “Graft-versus-host disease in allogeneic marrow transplantation”, in Biology of Bone-Marrow Transplantation, Gale and Fox, editors, Academic Press, N.Y., p 37.
To protect patients from such fatal damages, various immunosuppressive agents have been employed. Currently, allograft rejection is controlled using immunosuppressive agents such as cyclosporin A, azathioprine, corticosteroids including prednisone, and methylprednisolone, cyclophosphamide, and FK506. Cyclosporin A, the most powerful and most frequently used immunosuppressant, revolutionized the field of organ transplant surgery. Other immunosuppressive agents such as FK506, rapamycin, mycophenolic acid, 15-deoxyspergualin, mimoribine, misoprostol, OKT3 and anti-IL-2 receptor antibodies, have been used in the treatment and/or prevention of organ transplantation rejection. Briggs, Immunology letters, 29(1–2), 89–94, 1991; FASEB 3:3411, 1989. Although the development of new immunosuppressive drugs has led to substantial improvement in the survival of patients, these drugs are associated with a high incidence of side effects such as nephrotoxicity and/or hepatotoxicity.
For example, cyclosporin A has associated toxicities and side effects when used even at therapeutic doses. Although FK506 is about 10 to 100 times more potent than cyclosporin A in inhibiting activation-induced IL-2 transcription in vitro and graft rejection in vivo, it also shows side effects such as neurotoxicity and nephrotoxicity. Thus, there still exists the need for treatment and prophylaxis for GVHD with improved toxicity profiles.